1. Field of the Invention
The present invention relates to a perpendicular magnetic recording medium and to a magnetic recording and reproducing apparatus which are used for hard disk drives (HDD) or the like.
Priority is claimed on Japanese Patent Application No. 2010-189729, filed Aug. 26, 2010, the content of which is incorporated herein by reference.
2. Description of Related Art
The method of perpendicular magnetic recording is a method suitable for improving surface recording density since, in this method, axes of magnetization in the magnetic recording layer, which were aligned in the in-plane direction of the medium in the past, are aligned in the perpendicular direction to a medium easily, so that demagnetizing fields in the vicinity of magnetic transition regions, which are the borders between recording bits, become small; and therefore, the medium becomes more stable magnetostatically as the recording density increases, and thus the thermal fluctuation resistance is improved.
A perpendicular magnetic recording medium is manufactured by laminating a backing layer, an underlayer, an intermediate layer, and a perpendicular magnetic recording layer sequentially on a non-magnetic substrate. When the backing layer including a soft magnetic material is provided between the non-magnetic substrate and the perpendicular magnetic recording layer, the medium acts as a so-called perpendicular two-layered medium, and thus can obtain a high recording capability. At this time, the soft magnetic backing layer plays the role of reversing the recording magnetic field from a magnetic head, and thus can improve the recording and reproducing efficiency.
In addition, since the underlayer is a dominant element that determines the particle sizes or orientations of the intermediate layer and the perpendicular magnetic recording layer provided thereon, selection of the material is extremely critical in determining the recording and reproducing characteristics of a magnetic recording media. Therefore, a variety of materials are available as the underlayer. For example, it is possible to use an hcp-structured material or an fcc-structured material, such as a Ti alloy (for example, see Japanese Patent No. 2669529) or a NiFeCr alloy (for example, see JP-A-2003-123239), or an amorphous structured material, such as Ta. In addition, JP-A-2010-92525 describes the use of an alloy including, as the underlayer, one of Ni, Cu, Pt, and Pd as the main component and additive elements of one or more of Ti, V, Ta, Cr, Mo, and W.
It is suggested that Ru be used as the intermediate layer (see JP-A-7-244831). In addition, it is known that, since Ru has dome-shaped protrusions formed on the top portion of columnar crystals, Ru has an effect of growing the crystal particles of the recording layer or the like on the protrusions, promoting the isolated structure of the grown crystal particles, isolating the crystal particles, and thus growing magnetic particles in a columnar shape (see JP-A-2007-272990).